perl: warning: Setting locale failed

This error message happens after I did an upgrade to Debian 5.0 (lenny)

perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = (unset), LANG = "en_US.UTF-8" are supported and installed on your system. perl: warning: Falling back to the standard locale ("C").

dpkg-reconfigure locales

Then choose en_US.UTF-8 and it's fixed.